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299,792,458 metres a second -- that is the speed of light, but can we actually stop it
in its tracks? Firstly the speed of light is the cosmic speed
limit, nothing can go faster and in fact you can't even reach it because you're too heavy.
I mean massless particles like the photons that make up light go at that speed... except
when they don't. You might know that light actually doesn't
always drive around at the speed limit, it does in a vacuum, but when it's travelling
through other materials it tends to go slower. That's the very reason why swimming pools
look shallower than they actually are and how you're enjoying me right now over reams
of fibre-optic cable that we like to call the Internet.
In fact if you want to know a bit more about how the internet works check out James May's
video here. But even in those cases light is going pretty
damn fast. Recently though some researchers in Germany
have been able to stop light in its tracks, for a whole minute
Now I know a minute doesn't sound like a very long time but for light it is. Remember, in
that time it would normally travel the equivalent of 450 times around the Earth.
So how do you put the cooler on light? What you need is a glass-like crystal, two
lasers and some praseodymium ions. Now those charged particles in the crystal
make it opaque which means light can't get in or get out of the crystal, except when
you use your first laser. By firing a beam at the crystal a quantum
effect called "electromagnetically induced transparency" occurs, basically that allows
light of a very specific colour to get through. Enter laser number two, which just so happens
to have light of that very specific colour, so it can travel through the crystal but the
trick then is to turn off the first laser, which makes the crystal opaque and traps the
light inside the crystal. In fact the light inside the crystal isn't
really light anymore, it's a spin wave. Basically those praseodymium ions, because they have
electrons orbiting around the nucleus, have something called spin which makes them a bit
like a bar magnet. Now if you wiggle one of those bar magnets it's going to interact with
all the other ones, causing the nearest one to wiggle and the next one to wiggle and so
on so you get this wave of all these bar magnet type particles, and that is what our light
has been turned into.
But we can retrieve the original light from the crystal and that's exactly what the researchers
did after that minute. What's even better is that it retains its quantum coherence,
which essentially could be the new way of storing information. So in the future this
very video could be frozen light trapped inside a crystal which you could then access at super-fast
speeds. That's basically Kryptonian technology from Superman!
Because really the internet, I don't want to spoil the fun here, is like a giant telephone
network with cables and wireless devices connecting people and devices to the internet all over
the world.